Self-directed Solo Roth 401k investments

[Kia Afshar]

I will have a SD Roth Solo 401k at the end of this year with funds. I understand that a Self-directed Solo 401k can invest in leveraged investments without the UDFI tax implications. If I were interested in investing on one of the online crowdfunding/syndication websites, what types of investments would be recommended to avoid UBIT. It seems that any investment that does not create "ordinary income" would be ok (for example - need to avoid fix n flip, wholesaling, and anything that sells a product). However, a long-term buy and hold or BRRRR would likely be OK. Any wisdom to help guide my search would be appreciated. Thanks.